11 Measuring Cerebral Blood Flow and Metabolism
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چکیده
The first well-recognized CBF studies on humans were performed by Kety and Schmidt in the 1940s using nitrous oxide (N2O) gas. The measurement of CBF was based on the principle that the rate of uptake and clearance of an inert diffusible gas is proportional to blood flow. The tissue concentration of the tracer at equilibrium must therefore be dependent on blood flow rather than diffusibility. The Kety and Schmidt equation can be used for calculating CBF using N2O, krypton-85 and xenon-133. In fact, complete equilibrium of N2O between arterial blood, brain tissue and venous blood occurs slowly or not at all. Thus CBF calculated from a short saturation period will overestimate CBF (Hoyer, 1985). The Kety and Schmidt equation (1948) is:
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